#define _CRT_SECURE_NO_WARNINGS 1

#include<stdio.h>
#include<string.h>
#include<stdbool.h>

bool IsRepeat(char* arr, int n)
{
    for (int i = 0; i < n; i++)
    {
        int count = 0;
        for (int j = 0; j < n; j++)
        {
            if (arr[i] == arr[j])
            {
                count++;
            }
        }
        if (count >= 2)
        {
            return true;
        }
    }
    return false;
}

int main()
{
    char arr[102] = { 0 };
    scanf("%s", arr);
    if (IsRepeat(arr, strlen(arr)))
    {
        printf("NO\n");
    }
    else
    {
        printf("YES\n");
    }

    return 0;
}